The present invention relates to a bifurcated stent and to a method for the manufacture and delivery of a bifurcated stent.
Stents are generally known. Indeed, the term xe2x80x9cstentxe2x80x9d has been used interchangeably with terms such as xe2x80x9cintraluminal vascular graftxe2x80x9d and xe2x80x9cexpansible prosthesisxe2x80x9d. As used throughout this specification the term xe2x80x9cstentxe2x80x9d is intended to have a broad meaning and encompasses any expandable prosthetic device for implantation in a body passageway (e.g., a lumen or artery).
In the past six to eight years, the use of stents has attracted an increasing amount of attention due the potential of these devices to be used, in certain cases, as an alternative to surgery. Generally, a stent is used to obtain and maintain the patency of the body passageway while maintaining the integrity of the passageway. As used in this specification, the term xe2x80x9cbody passagewayxe2x80x9d is intended to have a broad meaning and encompasses any duct (e.g., natural or iatrogenic) within the human body and can include a member selected from the group comprising: blood vessels, respiratory ducts, gastrointestinal ducts and the like.
Initial stents were self-expanding, spring-like devices which were inserted in the body passageway in a contracted state. When released, the stent would automatically expand and increase to a final diameter dependent on the size of the stent and the elasticity of the body passageway. Such stents are known in the art as the Wallstent(trademark).
The self-expanding stents were found by some investigators to be deficient since, when deployed, they could place undue, permanent stress on the walls of the body passageway. This lead to the development of various stents which were controllably expandable at the target body passageway so that only sufficient force to maintain the patency of the body passageway was applied in expanding the stent.
Generally, in these later systems, a stent, in association with a balloon, is delivered to the target area of the body passageway by a catheter system. Once the stent has been properly located (the target area of the body passageway can be filled with a contrast medium to facilitate visualization during fluoroscopy), the balloon is expanded thereby expanding the stent, e.g. by plastic deformation of the stent structure, so that the latter is urged in place against the body passageway. As indicated above, the amount of force applied is at least that necessary to maintain the patency of the body passageway. At this point, the balloon is deflated and withdrawn within the catheter, and subsequently removed. Ideally, the stent will remain in place and maintain the target area of the body passageway substantially free of blockage (or narrowing).
A stent which has gained some notoriety in the art is known as the Palmaz-Schatz(trademark) Balloon Expandable Stent (hereinafter referred to as xe2x80x9cthe Palmaz-Schatz stentxe2x80x9d). This stent is discussed in a number of patents including U.S. Pat. Nos. 4,733,665, 4,739,762, 5,102,417 and 5,316,023, the contents of each of which are hereby incorporated by reference.
Another stent which has gained some notoriety in the art is known as Gianturco-Roubin Flex-Stent(trademark) (hereinafter referred to as xe2x80x9cthe Gianturco-Roubin stentxe2x80x9d). This stent is discussed in a number of patents including U.S. Pat. Nos. 4,800,882, 4,907,336 and 5,041,126, the contents of each of which are hereby incorporated by reference.
Other types of stents are disclosed in the following patents:
U.S. Pat. No. 5,035,706 (Gianturco et al.),
U.S. Pat. No. 5,037,392 (Hillstead),
U.S. Pat. No. 5,147,385 (Beck et al.),
U.S. Pat. No. 5,282,824 (Gianturco),
Canadian patent 1,239,755 (Wallsten), and
Canadian patent 1,245,527 (Gianturco et al.), the contents of each of which are hereby incorporated by reference.
All of the stents described in the above-identified patents share the common design of being mono-tubular and thus, are best suited to be delivered and implanted in-line in the body passageway. These known stents are inappropriate for use in a bifurcated body passageway (e.g. a body passageway comprising a parent passageway that splits into a pair of passageways). Further, these stents are inappropriate for use in a body passageway having side branches since: (i) accurate placement of the stent substantially increases the risk to the patient, (ii) the risk of passageway closure in the side branches is increased, and (iii) the side branches will be substantially inaccessible.
Indeed the Physician Guide published in support of the Palmaz-Schatz stent states on page 32 (the contents of which are hereby incorporated by reference):
xe2x80x9c . . . no attempt should be made following placement of a PALMAZ-SCHATZ stent to access the side branch with a guide wire or a balloon, as such attempts may result in additional damage to the target vessel or the stent. Attempts to treat obstructed side branches within stented segments can result in balloon entrapment, necessitating emergency bypass surgery.xe2x80x9d
Thus, when installed, the Palmaz-Schatz stent admittedly shields side branches emanating from the target area of the body passageway effectively permanently. This can be problematic since the only way to treat blockage or other problems associated with the side branches is to perform the type of surgery which installation of the stent was intended to avoid.
This contraindication for conventional mono-tubular stents is corroborated by a number of investigators. See, for example, the following:
1. Interventional Cardiovascular Medicine: Principles and Practice (1994); Publisher: Churchill Livingstone Inc.; pages 221-223 (Ohman et al.), 487-488 (Labinaz et al.), 667-668 (Bashore et al.) and 897 (Bailey et al.), including references cited therein;
2. Gianturco-Roubin Flex-Stent(trademark) Coronary Stent: Physician""s Guide; page 2, Paragraph 3 under WARNINGS;
3. Circulation, Vol. 83, No. 1, January 1991 (Schatz et al.); entitled xe2x80x9cClinical Experience With the Palmaz-Schatz Coronary Stentxe2x80x9d; pages 148-161 at page 149; and
4. American Heart Journal, Vol. 127, No. 2, February 1994 (Eeckhout et al.); entitled xe2x80x9cComplications and follow-up after intracoronary stenting: Critical analysis of a 6-year single-center experiencexe2x80x9d; pages 262-272 at page 263,
the contents of each of which are hereby incorporated by reference.
Further, some investigators have attempted to install individual stents in each branch of the bifurcated body passageway. However, this approach is fraught with at least two significant problems. First, implantation of three individual stents, together with the expansive forces generated upon implantation results in subjecting the central walls of the bifurcated body passageway to undue stress which may lead to post-procedural complications. Second, since the central walls of the bifurcated body passageway are not supported by the individual stents, this area of the passageway is left substantially unprotected and susceptible to blockage.
One particular problem area with bifurcated body passageways is the occurrence of bifurcation lesions within the coronary circulation. Generally, these legions may be classified as follows:
See Atlas of Interventional Cardiology (Popma et al.), 1994, pages 77-79, the contents of which are hereby incorporated by reference. The presence of bifurcation lesions is predictive of increased procedural complications including acute vessel closure.
Detailed classification of other bifurcated body passageways is relatively undeveloped given the lack of non-surgical treatment approaches.
U.S. Pat. No. 4,994,071 (MacGregor) discloses a bifurcating stent apparatus. The particular design incorporates a series of generally parallel oriented loops interconnected by a sequence of xe2x80x9chalf-birchxe2x80x9d connections. The lattice structure of the illustrated stent is constructed of wire. The use of such wire is important to obtain the loop structure of the illustrated design. The use of a wire loop construction is disadvantageous since it is complicated to manufacture and the resulting stent is subject to expansion variability (e.g. variable post-expansion distortion and the like).
U.S. Pat. Nos. 3,993,078 (Bergentz et al.) and 5,342,387 (Summers) also disclose and illustrate a bifurcated stent design constructed of wire. These designs suffer from the same disadvantages as the design described in the previous paragraph.
It would be desirable to have a reliable, expandable bifurcated stent since this would be useful in treating aneurysms, blockages and other ailments. It would be further desirable to have a practical method for producing such a stent. It would also be desirable if such a stent was relatively easy to install.
It is an object of the present invention to provide a novel expandable bifurcated stent which obviates or mitigates at least one of the above-mentioned disadvantages of the prior art.
It is another object of the present invention to provide a novel method for the manufacture of an expandable bifurcated stent.
It is another object of the present invention to provide a novel method for implanting an expandable bifurcated stent.
Accordingly, in one of its aspects, the present invention provides an expandable bifurcated stent comprising a proximal end and a distal end in communication with one another, the proximal end comprising a primary passageway and the distal end comprising a pair of secondary passageways, each secondary passageway in communication with the primary passageway at a first intersection, the stent being expandable from a first, contracted position to a second, expanded position upon the application of a radially outward force exerted on the stent, each of the primary passageway and the secondary passageways being constructed of a tubular wall having a porous surface, at least one connection portion being disposed at the first intersection for reinforcing the first intersection.
In another of its aspects, the present invention provides expandable bifurcated stent comprising a proximal end and a distal end in communication with one another, the proximal end comprising a primary passageway and the distal end comprising a pair of secondary passageways, each secondary passageway in communication with the primary passageway at a first intersection, the stent being expandable from a first, contracted position to a second, expanded position upon the application of a radially outward force exerted on the stent, each of the primary passageway and the secondary passageways having a porous surface, at least one connection portion interconnecting the pair of secondary passageways for reinforcing the first intersection.
In yet another of its aspects, the present invention provides a method for production of a bifurcated stent comprising the step of connecting a first stent section to a second stent section, the first stent section having an end thereof adapted for connection to an opening disposed along the length of a second stent section.
In yet another of its aspects, the present invention provides a method for production of a bifurcated stent comprising the steps of:
(i) connecting a first stent section to a second stent section to provide a connection portion;
(ii) provide an opening in the connection portion;
(iii) connecting a third stent section to the connection portion.
In yet another of its aspects, the present invention provides a method for production of a bifurcated stent comprising the steps of:
passing a first stent section having a first opening disposed along a length thereof through a second stent section having a second opening disposed along a length thereof, the first stent section having a diameter less than a diameter of the second stent section;
passing a leading end of the first stent section through the second opening of the second stent section; and
substantially aligning the first opening and the second opening with respect to one another.
In yet another of its aspects, the present invention provides a method for delivery to a target body passageway of an expandable bifurcated stent comprising a proximal end and a distal end in communication with one another, the proximal end comprising a primary passageway and the distal end comprising a pair of secondary passageways, the stent being expandable from a first, contracted position to a second, expanded position upon the application of a radially outward force exerted on the stent, each of the primary passageway and the secondary passageway being constructed of a tubular wall having a porous surface, the method comprising the steps of:
disposing the stent in the first, contracted position on a catheter;
inserting the stent and catheter within the target body passageway by catheterization of the target body passageway;
exerting a radially outward expansive force on the stent such that the stent assumes the second, expanded position and is urged against the target body passageway.
Thus, an aspect of the present invention relates to the provision of an expandable bifurcated stent constructed of a tubular wall having a porous surface. As used throughout this specification, the term xe2x80x9ctubular wallxe2x80x9d, when used in relation to a stent, is intended to mean a substantially cylindrical tube which subsequently has been subjected to an etching (e.g. by laser, chemical or other suitable means) or similar technique to remove pre-selected portions of the cylindrical tube thereby providing a porous surface on the tubexe2x80x94this is distinct from a stent constructed of wire bent to a selected shape/design. To the knowledge of the Applicant""s, an expandable bifurcated stent having such a tubular wall has heretofore been unknown.
As used throughout this specification, the term xe2x80x9cbifurcated stentxe2x80x9d is intended to have a broad meaning and encompasses any stent having a primary passageway to which is connected at least two secondary passageways. Thus, trifurcated stents are encompassed herein. Further, one of the secondary passageways can be a continuation of the primary passageway with the result that the other secondary passageway is essentially a side branch to the primary passageway.
The Applicant""s have also discovered that various repeating patterns in the porous surface of the tubular wall are particularly advantageous. Generally, the repeating pattern is a polygon having a pair of side walls substantially parallel to the longitudinal axis of the stent passageway in question, a first concave-shaped wall and a second convex-shaped wall connecting the side walls. The various repeating patterns which are useful in the context of the present invention are disclosed in the following copending patent applications filed in the name of the assignee of the present invention:
Canadian patent application number 2,134,997 (filed Nov. 3, 1994);
Canadian patent application number 2,171,047 (filed Mar. 5, 1996);
Canadian patent application number 2,175,722 (filed May 3, 1996);
Canadian patent application number 2,185,740 (filed Sep. 17, 1996);
International patent application PCT/CA97/00151 (filed Mar. 5, 1997); and
International patent application PCT/CA97/00152 (filed Mar. 5, 1997);
the contents of each of which are hereby incorporated by reference (hereinafter collectively referred to as the xe2x80x9cDivysio patent applicationsxe2x80x9d).
The present bifurcated stent may be constructed from any suitable starting material. Preferably, the starting material is a thin tube of a metal or alloy (non-limiting examples include stainless steel, titanium, tantalum, nitinol, Elgiloy, NP35N and mixtures thereof) which would then have sections thereof cut or etched out to leave a repeating pattern, inter alia, such as one or more of those disclosed in the Divysio patent applications.
The stent of the present invention may further comprise a coating material thereon. The coating material may be disposed continuously or discontinuously on the surface of the stent. Further, the coating may be disposed on the interior and/or the exterior surface(s) of the stent. The coating material may be one or more of a biologically inert material (e.g. to reduce the thrombogenicity of the stent), a medicinal composition which leaches into the wall of the body passageway after implantation (e.g. to provide anticoagulant action, to deliver a pharmaceutical to the body passageway and the like) and the like.
The stent is preferably provided with a biocompatible coating, in order to minimize adverse interaction with the walls of the body vessel and/or with the liquid, usually blood, flowing through the vessel. The coating is preferably a polymeric material, which is generally provided by applying to the stent a solution or dispersion of preformed polymer in a solvent and removing the solvent. Non-polymeric coating material may alternatively be used. Suitable coating materials, for instance polymers, may be polytetraflouroethylene or silicone rubbers, or polyurethanes which are known to be biocompatible. Preferably, however, the polymer has zwitterionic pendant groups, generally ammonium phosphate ester groups, for instance phosphoryl choline groups or analogues thereof. Examples of suitable polymers are described in published International patent applications WO-A-93/16479 and WO-A-93/15775. Polymers described in those specifications are hemo-compatible as well as generally biocompatible and, in addition, are lubricious. When a biocompatible coating is used, It is important to ensure that the surfaces of the stent are completely coated in order to minimize unfavourable interactions, for instance with blood, which might lead to thrombosis.
This good coating can be achieved by suitable selection of coating conditions, such as coating solution viscosity, coating technique and/or solvent removal step.